A Light polarization in charged exciton in Voigt configuration

I'm studying a charged exciton system, composed by two ground states (electron spin up 1/2 and down state -1/2) and the two heavy hole trion state (up 3/2 and down -3/2). In this case the light which couples two ground states and the trion state has right/left polarization, to conserve the spin. By turning on a magnetic field in the x direction, breaking so the rotational symmetry, the spin are aligned toward x and so becomes a superposition of the spin states along z, allowing an optical transition vertically polarized, and no more right circularly. Even expanding the x-basis eigenstates in the z-basis it's not clear for me how this vertical polarization transition come out. Is there anyone who could help me? thanks!

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